Samples based on the barium fluorobromide (BaFBr) host lattice were prepared in a pure form and doped to 0.5mol% with KF, KBr, SrF<sub>2</sub>, SrBr<sub>2</sub> and with several rare earth chlorides (EuCl<sub>2</sub>, LaCl<sub>3</sub>, CeCl<sub>3</sub> and SmCl<sub>3</sub>). Compounds with stoichiometric variations on the pure and europium doped barium fluoroiodide (general formula BaF<sub>1</sub>I<sub>1-x</sub>(:Eu<sup>2</sup>) where x = 0, 0.25, 0.50, 0.75 or 1) were also synthesised. In addition, the alkali halides NaBr, KBr and RbBr were doped with approximately 0.5mol% of both EuCl<sub>2</sub> and InCl. Emission generally occurred at wavelengths between 360nm and 450nm for these materials. None of them had room temperature emission bands that were as intense and narrow as that of BaFBr:Eu<sup>2+</sup>, because they do not have electronic transitions that are so closely matched to the electron/hole recombination energy as the 4f<sup>6</sup> 5d<sup>1</sup> → 4f<sup>7</sup> transition in Eu<sup>2+</sup>. TL glow curves showed a broad high temperature peak which arose as a result of charged defect migration and a variety of lower temperature peaks that were due to recombination from defect states within the band gap. The F(F') centre was matched to the glow curve peak t 400K and the F(Br<sup>-</sup>) centre to the lower temperature peak at 370K in a variety of mixed stoichiometry BaFBr-type compounds. It was also observed that a small amount of oxygen within the lattice appeared to enhance the intensity of a couple of the low temperature glove curve peaks, but too much oxygen had the opposite effect and these peaks were quenched. The time dependence of the intensity of PSL at timescales of the order of 100 - 6000 seconds was found to obey a power law decay from 100K to 300K. This could be modelled using random walk kinetics for the migration of the charged defect species. Upon irradiation and photostimulation at low temperatures an increase in the initial intensity of the luminescence and of the magnitude of the gradient of the linear plot was observed. This suggested that more change was stored at low temperatures and that new photostimulable centres were able to form more easily.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660298 |
| Date | January 2000 |
| Creators | Palmer, Carolyn M. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15578 |
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